The Linkage Between Up Dip Extension and Down Dip Compression in the Development of Toe Thrust Structures in the Deep-Water Gulf of Mexico

Kenneth J. Thies and James W. Granath
Maersk Oil America, Houston, TX

Seismic data and well control from the offshore Western Gulf of Mexico (GOM) provide interesting insight into the geometric linkage between and timing of up-dip shelf edge extension and down-dip compression in deep water. Imaging of the sub-salt structure of the deepwater slope in the GOM is generally obscured by shallow, relatively young allochthonous salt bodies. The Padre Island and Port Isabel Protraction Areas, on the other hand, provide an opportunity to view this connection where the salt although intimately involved does not regionally overlie the section. Models developed in this area can be useful to understand and guide predictions about the structure in other poorly imaged sub-salt areas.

Ultra-deepwater exploration in the GOM had been very limited prior to the discovery in recent years of thick hydrocarbon-bearing Late Paleocene/Early Eocene strata. Numerous salt cored antiformal structures are now being drilled with success rates of 65-70%. Many of these structures are located outboard of or near the leading edge of thick shallow salt, which complicates their connection to up-dip extension and thus adds to their risk as future exploration targets.

In the Port Isabel area, there is strong evidence that there was involvement of significant allochthonous salt sheets in the linkage between up-dip extension and down-dip contraction. A backstripping reconstruction of the section reveals a complex history of linked growth faulting and thrusting some of which was nested inside, e.g. inboard of the deformation front, and that some of the extension has been variously accommodated by salt flowage and deflation.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery